Transient post-mating inhibition of behavioural and central nervous responses to sex pheromone in an insect

Mating is costly for both male and female insects and should therefore only occur if it is likely to be successful. Within one scotophase, which is th e dark period of the light cycle, male moths can only produce one single sp ermatophore, which is transferred to the female during mating. Remating wit hin the same scotophase would thus be unsuccessful. We tested the hypothesi s that newly mated males of the moth Agrotis ipsilon have developed an ener gy-saving strategy based on the transient inhibition of their sexual behavi our, thus avoiding unsuccessful remating. Agrotis ipsilon males do not copu late more than once during the same scotophase. Moreover, newly mated males do not respond behaviourally to the female sex pheromone although electroa ntennograms showed that their peripheral olfactory system is fully function al. However, intracellular recordings of antennal lobe neurons showed that the sensitivity for the synthetic sex pheromone blend decreased as compared with that of unmated males. Both the sexual behaviour and the sensitivity of the antennal lobe neurons were restored when tested during the next scot ophase. Our results show a fast, transient neuronal plasticity that 'switch es off' the olfactory system, which could prevent males from mating unsucce ssfully.